brake job fail

[steveo]

why does it seem like brakes are way more of a whore than an entire sbc rebuild??

when i took the car for a drive the first time, you had to STAND on the brakes to even get it to slow down. took like 200+ feet to stop from 40kph. i was hoping that a few heat cycles would improve things, so i drove it around, hauled it down some hills in neutral and dragged them, and it never got better.

figured calipers were seized up or something, so i changed front rotor/calipers/pads, and rear rotors/pads, and i moved the rear pistons in and out a bunch of times to make sure they're free. (i woulda replaced them too, but they're like $100 each)

cleaned out the master cyl. tank, pushed a quart of fresh fluid through it just in case of crud in the system. the pedal pumps up fine and doesn't seem squishy or anything, and fluid got to the bleeders ok, so i dont think its a pinched line..

but it takes just as much force to stop the damn thing as it did before!?

what else could it be? could the brake booster be dead? im running out of ideas

just an extra kick in the gut, a rear wheel stud snapped off when i was retorquing the wheels. they're just a press-in stud that's easy to get to on these things, right?

[camarojokester]

I dont know if you completely removed all of the brakes or not but make sure the bleeders are facing up.

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[camarojokester]

To test the brake booster put your foot on the brake pedal abd start the car. If you feel the pedal move then its good.

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[steveo]

yeah, it moves

bleeders are facing up

im pretty lost, maybe something stuck up in the abs system is doing it?

[Scrub88]

So the pedal is nice and firm I had a similar problem with my Toyota truck i was chasing my tail and it ended up being the master cylinder had an internal seal failure it would let brake fluid squeeze around the seals internally but never leak ..I just couldn't get pressure to my calipers .
Maybe a machine vacuum bleed may help sense there's all the extra abs valving and lines

[R3DLT1]

My first thought was the brake booster to but u checked it n said it was good. Is there any visible fluid on take brake booster from the MC? The issue could also be internal from the MC.


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[steveo]

i havent actually tested the brake booster to see if it holds vacuum.. so it's still a suspect.

just because the pedal sinks a little bit when vacuum is applied doesn't mean it's actually doing its job, right? it doesnt sink very much, maybe an inch i guess

now that i think of it, a howling noise in the cabin has developed.. seems to be coming from the firewall, and doesn't seem to be drivetrain related

that could be a leak in the brake booster right? happens when the car is at a dead stop, its definitely not wind..

i dont really know much about how they work

you'd figure a master cyl that's blown would feel spongy or weird, and my pedal feels hard as hell

could something in the abs module ever cause behavior like this?

[Greed4Speed]

How much vacuum do you have?

[Scrub88]

That sounds like brake booster to me the noise of it pulling air thru a worn seal and a hard pedal is a sign of failing booster

[steveo]

last datalog showed ~30 kpa at idle, which actually seems a bit high considering how mild the cam is

it does idle really shitty, so something is up. i got a booster from the wreckers, i'll put it in and hope for the best

[steveo]

plugged the brake booster line, started the car, and it barely started at first. idle was 500rpm lower and much more stable than usual

so i put a hand vac. pump on the old brake booster, and i couldn't even get an inch of vacuum out of it

i guess it's dead

i got the old one unbolted just fine, but i gave up trying to get it out of the engine bay. it just wont fit. looks like i have to pull the drivers side header or something. nasty...

anyone know any tricks?

[Greed4Speed]

Cutting torch and a big hammer

[steveo]

dont tempt me to pioneer a brake booster trapdoor mod

seriously though its huge, its going to be a bitch to get out

[R3DLT1]

Since we r in the topic of brake.boosters n all i had.a car come in.at the shop for s hizzing sound coming from the brake pedal when being pressed.... Bad brake booster... The diaphragm in the booster is leakg internally?

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[Scrub88]

If its hissing try Steveos method and hook a vacuum pump to it . If it ain't holding then yea bad . I dunno Steveo on pulling one out from the looks of it it's gonna be a squeeze . Gm didn't cut any slack on making these things easy